Prop Size ?

Survey report should have stated what was read on the wheels.
What option engines do you have?

If the props do not have cup, a fairly accurate method is to measure the blade height at 2/3 diameter and at the same place, of the measurement, measure the degrees of the blade, the degrees divided into 360 times the height gives you the pitch. Easy to do when prop is off but it can be done installed. I just had mine repitch, as Capt Ralph said the props should be marked as mine were but mine came in 1 inch less than they were marked. My explanation may be hard to comprehend but if you search the internet you will find a more detail presentation.

Removal and measurement by a prop shop is the only accurate way to measure pitch, AFAIK.
Never heard of the system Capt Fred mentioned, and while it doesn't sound very accurate to me, maybe it is - IDK.

There's another thing that grabbed my attention in your photo, though: no anodes anywhere on the u/w gear (rudders/struts/shafts/props).
I see the centerline anodes astern, which I assume are connected to the engines, as per MAN installation standards.
But even if they were grounded together with all the u/w gear (which is not what MAN recommend, BTW), it's good practice to fit dedicated anodes anyway, to my knowledge.

PS: diameter doesn't help at all in estimating pitch, but if you would post your max speed+rpm, and also the gearbox ratio, it would be possible to make a (very rough!) pitch estimate.

It's not good to over zinc a boat. That can also create galvanic corrosion issues. If it is all designed to go to a plate and all connections are good, leave it that way.

Never heard of to muck zinc.

Here are some great FAQs on this subject;
Scroll down to the TECHNICAL section
https://www.boatzincs.com/faqs.html

Back to the prop OP;
Where did the surveyor get his data?
From the prop or a spec sheet?
Never known or know of a surveyor not to read the numbers off of the wheels.

Zinc Anode Failure | Boating Mag

Splash, when talking of boats, I'm a big fan of the "if it ain't broke don't fix it" principle, so I see your point.

OTOH, beware: stray current is a bïtch, that can potentially destroy all kind of metals PDQ.
Luckily, it's a (relatively) rare occurrence, so it's a problem that can well not exist in one particular berth, as well as in several others.
BUT, in another one, it could literally make props/rudders/struts/whatever fizz away in no time.
So, I wouldn't rely too much on the fact that the previous owner never came across such problem.

And with all due respect for your surveyors and MAN engineer, if you are sure that all the boat u/w protection relies on the single large anode visible in the photo, I can confirm you that such setup does NOT comply with MAN installation requirements, according to which nothing but the engine (which as opposed to other manufacturers has no anodes at all) should be connected to the external zinc astern. Actually, they go as far as suggesting that each engine should have its own dedicated zinc, though I've seen a single zinc connected to both engines in many MAN powered boats, mine included.

Besides, it's a well known principle that also the distance between the metal to be protected and the anode is relevant (i.e., it should be as short as possible). And even assuming that the shafts+props, struts, rudders, trim tabs are all properly bonded inside the hull to the single stern anode, it's rather obvious that the distances are MUCH longer, when compared to say the typical rudder bolted anode, or the one bolted just behind the prop hubs, or on the trim tabs plates, etc.

Lastly, I won't comment the fear of "over-zincing", because if you and Capt J take a minute to read carefully the Kevin Falvey article that he linked, you will realize that the possible problems are literally laughable, when compared to the risks of insufficient protection.

I was not to impressed with that article either.

My 44 year old Bertram has shaft and tab zincs.
Pending what was tied next us, these zincs lasted a month to over a year.

Ah, the value of a diver, zinc maintenance and confirmation of that floating pile of problems in the next slip.
Yep, sometimes, 2 zincs per shaft till that pile of problems was away from our boat.

Over zinc?? Not close..
44 year old equipment in good shape?? Priceless..

Absolutely.
BTW, when I called the risks laughable in comparison to lack of anode protection, it was according to what he wrote himself.
But in decades of boating, I've yet to come across any surveyor or engineer suggesting to fit smaller anodes - let alone remove them!

The single zinc absolutely does and has satisfied MAN installation requirements. Cabo and Viking have been building thousands of MAN boats for years with just a transom zinc as well as many other builders.

There are other problems with over-zincing and I could find a better article but aluminum wasting away is one of the big issues and one of the metals in S/S making the S/S brittle is another. The fact that you've never heard of over-zincing, or have never seen thousands of MAN powered yachts built with a single transom zinc is rather concerning. Perhaps you should do your homework, instead of spouting expertise where you have none.

Here
Over-Zincing. Any horor stories from too much protection? - Cruisers & Sailing Forums (cruisersforum.com)

J
I'll let the experts argue about the MAN requirements.
What few MAN boats we assisted on, had shaft zincs, no idea who's requirement it was.

But now your digging up old junk from the junk yard.

I'll agree that zincs and high copper & mixed metals paint react. Don't think that's over zinc, just ship happens between zincs and high metal paint.
Poor paint application may have been a junk yard issue also.

But when all wet metals are bonded, I will never believe that anything bad could happen on a plastic boat with a few zincs properly installed.

Of course, were not talking about hanging hundreds of pounds of zinc either.
Just a lil extra on the gear in case the owner jets tied up close to one of those pile of problems, I'm sure we are all aware are still out there.

Absolutely great to have an isolator on board. They do greatly reduce galvanic erosion in a marina environment.
I'm not trying to talk you into anything. Just continuing that an extra zinc is not going to hurt anything as over zincing.
Also, A good diver schedule is also a great PM tool.

CJ, I have two very simple questions for you.

First, why don't you actually read the posts, before commenting them?
Me: "I've seen a single zinc connected to both engines in many MAN powered boats, mine included".
You: "The fact that you [...] have never seen thousands of MAN powered yachts built with a single transom zinc is rather concerning".
Whiskey Tango Foxtrot?!?

Besides, my point was that MAN prescribe that the engine should be connected to the transom zinc alone, which means lack of protection for the rest of the u/w gear (unless fitted with some other zincs as appropriate), rather than for the engine itself.
I'm not sure of which part of this is so hard to understand.

Second, why don't you read also the content of the webpages that you find, before linking them?
See, these days nobody need your help for throwing "over-zincing" into Google and see what it comes up with.
And as well as with your previous link, also this one does NOT actually support your claims, if you bother to actually read it, rather than just linking it.

Lastly, and this isn't a question but just a comment for your consideration, I couldn't care less about "selling" my own expertise, since boating is for me nothing more than a hobby, and I have no horse in this race - as opposed to yourself, as I understand.
Now, take this just as a 2c from someone whose hairs are surely whiter than yours: by accusing me (or anyone else) of spouting expertise where I have none, you are not doing yourself a favor.
In fact, that does NOT put you automatically in the position of having the expertise that you pretend someone else is lacking.
Also because linking meaningless webpages (let alone webpages actually supporting the opposite of what you are saying!) found with google is an expertise that is very unlikely to impress anyone.

My reference is the rest of the running gear. It is tied into the transom zinc. The shafts have shaft brushes that are in constrant contact with the shafts and connect to the transom zinc, some goes for rudders, they too are all bonded to the one zinc.

I know exactly what over zincing does as I hired an expert to measure a boat we had problems with and spent 3 entire days with him measuring every circuit, fitting, etc. throughout the yacht and asking questions. There should be a certain level of electric found on the meter between your bonding system and the water (as saltwater in itself is an electrolite). On Aluminum hulls you want to read the voltage on a silver chloride electrode connected to the metal it's .75-.9 volts, the US Navy specifies .85 volts on their hulls. Wood 0.5-0.6V or you'll cause caustic wood rot. Too much and obviously metals get attacked. Too little (overzinced) and it actually attracts stray electric current from the water and attacks different metals. Over zincing is really bad for aluminum hulls and steel hulls (it's cause the paint to lift right off of them) and wood (make the wood brittle). But on fiberglass it can kill the bottom paints effectiveness in a month or two. Also too many zincs, even with fiberglass will cause the zinc to develop a crust and stop protecting completely. There are plenty of articles out there who are experts in the field, I simply linked the first one I could find.

The problem at times, is you spout misinformation on some topics you clearly know nothing about, which can cost owners a lot of issues and expense. If you would like me to spend an hour of my time looking for articles that are more informative for you on over-zincing I would be more than happy to.

Can You Have Too Many Zincs? - Practical Sailor (practical-sailor.com)